Mobo Chipsets Define Crossfire or SLI?

Hey guys, I'm in need of some knowledge here.. Is it possible that a motherboard's chipset defines whether it supports SLi or Crossfire? If so, can any of you guys let me know which supports which?

Also on a side note, how can one know whether both PCI-E slots run at x16 bandwidth when both have cards inserted or if they rearrange into both x8/x8 (if not already specified in description)? Thanks in advance to any of you who can help me out .

Yes, normally only NVIDIA's nForce chipsets support SLI and Intel's X series and some of their P series chipsets support Crossfire. There are two exceptions to this, namely the DX5400XS (otherwise known as "Skulltrail") motherboard which supports SLI and Crossfire, and some motherboards based on Intel's latest X58 chipset which also support SLI and Crossfire.

As for the PCI-E slots running at x8+x8, don't bother. There are no cards that utilize the maximum bandwidth allotted by PCI-E 1.1, let alone 2.0, which is the PCI-E specification you'll find on mobos with newer chipsets like the Intel P45 or nForce 7xx series chipsets. In any case, these newer motherboards feature both of the PCI-E 2.0 slots running at x8 each, which is equal to two PCI-E 1.1 slots running at full speed, more than enough bandwidth for any card.